1 CFR § 601.17 - Supplemental Environmental Assessments.

---
identifier: "/us/cfr/t1/s601.17"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "1 CFR § 601.17 - Supplemental Environmental Assessments."
title_number: 1
title_name: "General Provisions"
section_number: "601.17"
section_name: "Supplemental Environmental Assessments."
chapter_name: "NATIONAL CAPITAL PLANNING COMMISSION"
part_number: "601"
part_name: "IMPLEMENTATION OF THE NATIONAL ENVIRONMENTAL POLICY ACT"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 4371; 40 CFR 1507.3"
regulatory_source: "82 FR 45424, Sept. 29, 2017; 82 FR 48609, Oct. 19, 2017, unless otherwise noted."
cfr_part: "601"
---


# 601.17 Supplemental Environmental Assessments.

(a) The NCPC shall prepare a supplemental EA if five or more years have elapsed since adoption of the EA and:

(1) There are substantial changes to the proposed action that are relevant to environmental concerns; or

(2) There are significant new circumstances or information that are relevant to environmental concerns and have a bearing on the proposed action or its impacts.

(b) The NCPC may supplement a Draft or Final EA at any time to further the purposes of NEPA.

(c) The NCPC shall prepare, circulate, and file a supplement to a Draft or Final EA, and adopt a FONSI in accordance with the requirements of §§ 601.15 and 601.16. If NCPC is not the Lead Agency, it shall proceed as outlined in § 601.16(b) and (c).